1. Field of the Invention
The present invention relates to a writable or rewritable optical information recording medium.
2. Description of the Prior Art
A writable or rewritable optical information recording medium such as an optical disk is normally provided with a groove for tracking, and depressions for storing address data and clock information, namely, in the form of pits, formed at the bottom of the groove. An area for the pits to store address data and the like are not usable as an area for recording information.
It is desirable to store as much address data as possible. However, the more the area devoted to the address data is increased, the more the area for the information is decreased. This results in reducing the capacity of the optical disk.
Recently, there has been proposed a writable optical disk D provided with a guide groove having a meandering mid-line of G.sub.1 and a constant amplitude A, as shown in FIG. 1A. The perspective view of the guide groove is shown in FIG. 1B, wherein both width W and depth t of the guide groove are kept substantially constant. The meandering of the guide groove is caused by a carrier wave which is frequency-modulated by an address data signal. Furthermore, the surface of the optical disk D where the guide groove is formed is coated with a recording layer such as of a dyestuff and the like (not shown) for providing writable or rewritable capability.
A process for fabricating an optical video disk or a compact disk can be applied to the manufacture of the writable optical disk D having such a guide groove without any modification.
In fabricating the optical disk D provided with such a guide groove, a major surface of a glass substrate is first covered with a photoresist film having a predetermined thickness by a spin coating process. The photoresist film is then exposed to a light beam such as an Argon laser beam, which is oscillated in accordance with a carrier wave, which is frequency-modulated by an address data, through an optical light beam deflector. Then the exposed photoresist film on the glass substrate is developed to obtain a master disk. A stamper is then prepared to make use of the master disk, and, in turn, a synthetic resin disk substrate produced by employing the stamper is covered with a recording layer and a protective layer for fabricating the optical disk D provided with the guide groove.
In the conventional writable optical disk D, additional data that can be multiplexed onto the guide groove are limited to two kinds of data, the address data and timing data. However, when the frequency of the carrier wave is utilized as the timing data, it is desired to record various kinds of information besides these data through a multiplex recording system in order to increase packing density.
It is therefore an object of the present invention to provide an optical recording medium having an increased packing density by recording various kinds of information onto a guide groove through the multiplex recording system.